The need to replace a damaged (or simply duplicate a) spectacle lens of a patient arises repeatedly in the vision care field. Often, the patient's eyeglass frames and other spectacle lens remain intact and undamaged. In these cases the practitioner merely removes the damaged lens from its frame (if necessary) and, with a writing instrument, traces either the frame socket or the circumference of the lens itself (if intact) onto a flat cutting blank. The blank, made typically of firm plastic, can then be cut along the marked circumference with scissors or a knife until its contour matches that of the lens or empty frame socket.
The contoured blank may then serve as a pattern from which a replacement lens can be made. Some edging machines, such as those described in the section of U.S. Pat. No. 4,693,034 entitled "BACKGROUND OF THE INVENTION" and whose structural attributes are incorporated herein by this reference, mount both the contoured blank and the replacement lens on a floating axle, causing the blank to function as a cam permitting the grinding surface to contact portions of the periphery of the replacement lens. Through many rotations of the lens the grinding surface selectively reduces the radius of the lens by grinding along its edge until the lens is contoured similarly to the blank.
Another machine, disclosed in U.S. Pat. No. 2,231,994 to Flattem, uses a follower and a diamond or wheel-equipped cutting tool to etch the outline of a lens on a face of a glass blank. Although the blank rotates as a hand crank is turned, the diamond tool does not rotate and the alternative etching wheels rotate only in response to movement of the blank. Moreover, because the cutting tool does not perforate the entire depth of the blank, after the outline is etched the practitioner or technician, using the outline as a guide, must separate (by breaking) the patterned portion of the blank from its remainder. The requirement of separating the portions of the blank manually increases the likelihood that discontinuities will be present in the contour of the blank near the reverse face as well as the possibility of injury to the practitioner, technician, or bystanders from sharp, broken glass.
U.S. Pat. No. 3,170,374 to Clar illustrates a pattern-producing apparatus for spectacle lenses using a spectacle frame socket as a template rather than the lens itself. The apparatus includes an end milling tool for cutting lateral entry groove or notch in a lens blank. After the groove is formed a motor activates to rotate both the blank and a guide roller within one frame socket, causing the effective cutting edge of the end milling tool to form the pattern in the blank. Utilizing a spectacle frame socket as the template is awkward and unwieldy, however, requiring radically eccentric rotation of the frame itself. The guide periphery and cutting edge of the end milling tool are also permanently aligned, precluding proportional sizing of the blank relative to the template.